Bank 1 Lean ...help
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This is a discussion on Bank 1 Lean ...help within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; So, I picked up a stock 03 WRX a few months ago that I am just using as a daily ...

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    Bank 1 Lean ...help

    So, I picked up a stock 03 WRX a few months ago that I am just using as a daily driver. The car runs fine, but it has a CEL light that had been on for a while, according to the previous owner. I finally got the time to investigate and get the code pulled and it read "Bank 1 Lean"... I didn't catch the actual code number. It has turned off for a while and come back on at least once since I've owned it. I've read a few things about this on other forums, but it's hard to find info on stock cars, because most people are throwing this code because of mods. The most interesting thing I found was a guy throwing this code because of a leak, and he said his turbo sounded like a stuck pig when spooling up. ...mine makes a noise I might compare to a stuck pig as well, but only under load. So, I'm think this might be a leak, but if there are other suggestions, I'm open.
    If it is a leak, how should I go about finding it and fixing it?
    Thanks!
    -Dr. P-

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    Registered User Ruh Roh's Avatar
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    You bought it with a CEL code or did it just happen? What are the mods?

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    It had the CEL when I bought it, and the owner told me it had be on for a while. ....so I know it has been on for a long time (probably 25k miles), but the car is still running fine, so I doubt we're dealing with a catastrophic problem. ...still, I'd like it fix it if I can.

    There are no mods.

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    ...I might add that I am family friends with the guy I got the car from, he's a 55 yr old guy that just used the car to get to work and home. It was never modded or raced, and it's serving the same purpose for me.

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    Registered User UEDan's Avatar
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    Re: Bank 1 Lean ...help

    A lean condition can melt pistons.

    Check for leaks.

    Posted from a fone.

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    He simply abides. SD_GR's Avatar
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    Be aware there is only 1 bank.

    If and only if "Bank 1 Lean" actually means PO171:

    Clean the MAF.
    Clean the air filter, or replace it.
    Check for intake leaks.
    Check for boost leaks.
    Check for fuel pressure regulator reference line leak.

    Search troubleshooting PO171 if so.

    What worries me most is your statement that it's stalled in the past. That's not typical for a PO171, which is usually the wrong intake with at least one leak plus a dirty filter and dirty MAF.
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    It has not stalled, sorry if I was unclear. I meant that the CEL itself has turned off for a little while and turned back on.

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    He simply abides. SD_GR's Avatar
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    Aha, OK, much better. Again, if and only if you saw PO171, troubleshoot as above. Is the car completely stock? No modifications?
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    No mods... except for a mishimoto radiator I put in because the stock plastic one had a hairline crack. It runs great, idle is perfect. There is a little bit of a funny noise under load when the turbo is spooling up, as I mentioned, and it seems like the power MIGHT be a little weak up high, but my other car is 700 RWHP, so I'm slightly biased on that one. I really never get on this car hard, it's just a commuter, and like I said, it has been running perfectly as a commuter.

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    He simply abides. SD_GR's Avatar
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    OK this all sounds like good news. The simplest fix for a PO171 is to clean the air filter, make sure the housing is seated in the tabs, make sure there are no vacuum lines loose etc., and clean the MAF with MAF cleaner (including into the MAF tube itself; the visible probe is for temp not air flow so you have to reach the other one but it's buried and it's also sensitive so tread very lightly etc.).

    There is the outside chance that the O2 sensor has an issue but I'd worry about that absolutely last.
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    Quote Originally Posted by SD_GR View Post
    OK this all sounds like good news. The simplest fix for a PO171 is to clean the air filter, make sure the housing is seated in the tabs, make sure there are no vacuum lines loose etc., and clean the MAF with MAF cleaner (including into the MAF tube itself; the visible probe is for temp not air flow so you have to reach the other one but it's buried and it's also sensitive so tread very lightly etc.).

    There is the outside chance that the O2 sensor has an issue but I'd worry about that absolutely last.
    Awesome, thank you!

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    Registered User gregroot198521's Avatar
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    Bank 1 Lean ...help

    I've been having the same issue lately. The P0171 code popping up the last couple weeks. Cleaned the Cobb cone filter and the MAF. We'll see tomorrow if this was the issue, I suppose. If it comes back, I'll have to check if I ****ed the pooch on the MAF, or if I need to continue hunting for the cause. So it'll be loose vacuum hoses next, possibly an O2 sensor, spark plugs, etc.... I found some old thread on NASIOC about this and those were some of the causes.
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    Admiral Ackbar the 1st mycologist's Avatar
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    SD covered this extremely well.

    Also,
    The clamps on the intake track in-between the MAF and the turbo are a primary culprit.

    A torn turbo inlet is a possibility - it can be hidden on the underside of the turbo coupling which is very hard to check.
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    ...maybe an amateur question, but I haven't been able to gather the answer from what I've read, and I don't have an AF gauge in the car to be able to tell... Does this code mean that unmetered air is going into the engine, and it is actually burning lean? ...or does it mean that more air is going in than should be and is burning more fuel accordingly? I have read that vacuum leaks cause an increase in fuel consumption, but that would suggest to me that the car is compensating. ...just wondering.

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    Admiral Ackbar the 1st mycologist's Avatar
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    Quote Originally Posted by Dr. P View Post
    ...maybe an amateur question, but I haven't been able to gather the answer from what I've read, and I don't have an AF gauge in the car to be able to tell... Does this code mean that unmetered air is going into the engine, and it is actually burning lean? ...or does it mean that more air is going in than should be and is burning more fuel accordingly? I have read that vacuum leaks cause an increase in fuel consumption, but that would suggest to me that the car is compensating. ...just wondering.
    Yes, my understanding is that excessive unmetered air is getting in, so it is burning lean, so the O2 sensor in the front is detecting that and the ECU is therefore unhappy. If it were metered air, there would be no issue as fueling would compensate.
    "From a little spark may burst a mighty flame." - Dante
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